Prosthetic heart valves have been used for replacing damaged heart valves in patients. Various types of prosthetic heart valves are known, including mechanical heart valves and bioprosthetic heart valves. One group of prosthetic heart valves may include a material such as tissue or synthetic polymers carried on a stent. The material typically comprises animal tissue such as porcine aortic valve material or bovine pericardium.
Various techniques are known for coupling the material to the stent. For example, suturing the valve material to the stent is one common technique used to couple the material to the stent. However, such suturing has been found to place stress on the material as the valve opens and closes, thus leading to a shorter useful life for the prosthetic heart valve. In fact, any attachment technique which creates a hole in the tissue near the post tips will concentrate destructive stresses in those areas.
Other types of attachment techniques are also shown in the prior art. For example, U.S. Pat. No. 4,501,030, issued Feb. 26, 1985, entitled "METHOD OF LEAFLET ATTACHMENT FOR PROSTHETIC HEART VALVES" describes the use of a clamping force to hold the material to the stent. However, the design uses sutures which are positioned near the top of each of the stent posts. Further, U.S. Pat. No. 4,501,030 focuses the clamping force in a small region of the material between the thin wire stent and a polymer clamping piece. By further concentrating the clamping force, the valve may be more likely to require early replacement. It may be possible to improve the performance of this device by increasing the area over which the clamping force is applied. In addition, this device applies stress to the leaflet material in direct relation to the closing load of the valve. U.S. Pat. No. 4,441,216 issued Apr. 10, 1984, entitled "TISSUE HEART VALVE AND STENT" describes the use of sutures along the top of each of the stent posts in order to attach the material to the stent. U.S. Pat. Nos. 5,163,955, 5,423,887 and 5,489,298 to Love all describe the use of alignment members at the tops of the posts. These alignment members put holes into the material. Further, the designs of Love are relatively complicated in that they require several pieces and use an inner and an outer stent which adds considerable thickness to the device. Similar problems are encountered in U.S. Pat. No. 4,725,274, to Lane which issued Feb. 16, 1988. The Lane patent requires four separate stent components which, when assembled, create a relatively thick stent.